1. Field of the Invention
The invention relates to bleach releasing particles and their use in mechanical dishwashing compositions.
2. The Prior Art
An important component of most commercial granular machine dishwashing detergents is bleach. Normally, the bleach component is a material having at least one reactive chlorine which will generate hypochlorite in solution. Chlorine bleach performs several functions including removing stains, sanitizing surfaces and degrading protein soils. Particularly critical is the protein soil degradation function because proteins are known to deposit on glassware leading to unsightly spots which consumers find objectionable.
Many types of chlorine bleaches are known to the art. They all, however, serve as a source of hypochlorite (more precisely hypochlorous acid) which is the active species. Hypochlorite, being a strong oxidizing agent, can interact with various sensitive ingredients of commercial machine dishwashing formulations. These ingredients include perfumes, dyes, surfactants and bases. Free water present in the formulation contributes further to the bleach reactivity with the aforesaid ingredients. These interactions lead to a gradual loss of chlorine available for chemical cleaning and a deterioration of the dishwashing performance. Instability is accelerated by storage at high temperature and/or humidity. Under such conditions, there may occur fading of product dye, fragrance deterioration and solubility decrease.
Although some hypochlorite sources are more stable than others, they all suffer at least some loss in available chlorine on storage. To minimize the drop in cleaning performance, it is common practice to overdose the bleach. Overdosing is not only costly but does not completely solve the stabilization problem. For instance, as much as 80% of the original chlorine content can be lost yet the bleach may still be potent enough to interact with other parts of the composition. Stabilization of chlorine bleach thus remains an important problem in machine dishwashing compositions. Furthermore, it must be noted that the chlorine bleach overdose approach still does not solve the problem of dye and perfume deterioration.
U.S. Pat. No. 3,112,274 (Morgenthaler et al.) discloses the use of inorganic salts such as sodium tripolyphosphate, applied in a fluidized bed, to coat polychloroisocyanurate bleach releasing salts. The resultant encapsulated salts are said to be protected from decomposition by the attack of moisture, and insulated from reacting with sensitive organic materials.
Organic coating materials have also been reported as encapsulates for chlorine bleaches formulated for laundry detergents. For instance, U.S. Pat. No. 4,136,052 (Mazzola) surrounds an active chlorinating agent with a first non-reactive coating combination of fatty acid and wax. A second coating is applied thereonto containing fatty acid with a material exhibiting inverse aqueous solubility with respect to temperature. The outer, second coating is more resistent to dissolution in hot than in cold water. Similarly, U.S. Pat. No. 3,908,045 (Alterman et al.) discloses dichloroisocyanurate salts encapsulated with a first coating of a saturated fatty acid surrounded by a second coating of soap.
From the foregoing, it can be seen that many coating agents have been disclosed in the literature to stabilize chlorine bleach for detergent compositions. The reported organic coatings have included fatty acids, soaps, waxes (e.g. paraffin wax and low molecular weight polyethylenes), and oily substances (e.g. dialkylphthalates). Unfortunately, these and other similar materials are unsuitable for machine dishwashing applications for several reasons.
Materials such as common fatty acids, which are soluble in an alkaline media, can produce excessive foam under the high agitation characteristic of the mechanical dishwasher. Fatty acids, waxes and oily substances that are insoluble in water can indeed stabilize chlorine bleach as is well known in the art. However, these coating materials release the bleaching agent through melting or cracking during the course of the wash cycle. Their release can therefore be erratic especially considering the short wash times and lower wash temperatures found with present day equipment. Furthermore, oily or waxy materials can act as a sink for oleophilic components in the formulation, e.g., nonionic surfactants and perfume components. Finally, water insoluble oils or waxes by their very nature are prone to deposit on dishes, glassware, or the dishwasher. Deposits are particularly objectionable to consumers.
Consequently, it is an object of the present invention to provide bleach particles which are sufficiently aggressive to clean dishes and glassware but are storage stable to high temperature, moisture and reactive detergent components.
A further object of this invention is to provide bleach particles that are sufficiently cleaning aggressive but nevertheless do not significantly interact with detergent co-components such as perfumes, dyes and surfactants.
A further object of this invention is to provide bleach particles which will generate little or no foam in detergent compositions subjected to conditions of mechanical dishwashing.
Another object of this invention is to provide bleach particles that substantially retain their available chlorine upon storage but upon dissolution in an aqueous alkaline solution quickly release active bleaching agent yet do not have the potential for detracting from glass appearance.